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Full Version: Pyro gauge. Inside or Outside? - My thoughts.
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I have seen lots of Owners Operators install pyrometers on their engines. I have seen lots of debate over where to put them and what to use them for. I thought I would post a few words on what I think about the placement of the pyrometer sensor/probe based on what I see others doing, and what I do myself, so here goes...

When it comes to installing a pyrometer gauge onto your engine, there a lot of ways to do so. Installing the probe in the manifold, past the turbo in the exhaust, or strapped to the outside of the manifold like in my gauge instillation videos. I have even seen guys who mount more than one probe, having one drilled into the manifold, and one strapped to the outside of it.

When considering where to put your pyrometer probe, this is what you need to ask yourself ...

* What am I hoping to measure/monitor?

* What do I plan on using that information for?


A pyro gauge is typically used for 2 things. Measuring the actual EGT's, or for measuring manifold/turbo heat accumulation.

The usefulness of tracking actual EGT's ...
- This is great for troubleshooting, watching exhaust temps if your using excess power levels in the engine (using more power, producing more heat than the engine is rated for), and useful if you do your own custom engine tuning. The ECM estimates this in the ISX engines and usually gets it close, but not always right. This becomes especially true if you have had some poorly done custom tuning. Lets first look at placement of the probe pre and post trubo...

- Pre-turbo (in the manifold) is preferred vs post turbo and is typically more accurate of what is coming out of the engine. This is what a person would want if they were doing their own troubleshooting or custom tuning for best accuracy. So... a person needs to ask themselves how often they are going to use this information over the lifespan of their truck as a driver or truck owner. -- Most would say very little actually, and after a few months,... They hardly ever look at the gauge again.

Care must be taken pre-turbo for the probe and the threaded hole, as it will suffer pounding from each cylinder as valves open/close, a lot of heat, and exhaust pressures that can reach 80-90 PSI or more. Any type of failure and it will typically take out the turbo along with it.

This leads back to my question... What are you hoping to measure, how important is it to be accurate vs relative, and what are you going to use this information for?

- Post turbo is the heat of the exhaust minus what has been absorbed by the turbo and is less accurate. It is a "safer" place to install a pyrometer gauge into the exhaust stream and pressures are low.

If your still looking to measure EGT's and accuracy is slightly less relevant, then post turbo is safer. it is also easier to do, as drilling a hole in the intake manifold requires the removal of the turbo to ensure shavings do not go through it after. An expensive turbocharger is not worth the "It will be ok" attitude in my book, as I would have to be the guy who paid the $3,000 for a new one if I did not get all the shavings out the first time. - I would call not pulling the turbo off before drilling, one of those "$3,000 mistakes" for sure, so it is generally "safer" to drill AFTER the turbo and install it there.


Now lets look at the usefulness of tracking manifold temps (probe strapped to the outside of the manifold) ...

- Manifold temps are a basic measure of "How much heat are you have built up in your engine/turbo overall". The ECM also tracks this. This is good for determining how hot you are making your turbocharger get, how much heat is being transferred into the oil, and how hard you are pushing/wearing your engine too.

With the probe on the outside of the exhaust manifold, the temp reading is usually about 50-75 degrees cooler than what is inside after the temp settles out (during a few minutes of steady climbing or other application). It can be as much as 100 - 130 degrees less than the actual EGT's if the engine fan is on and forcing air across the manifold/turbo. Some would say it is lying to you because of this, but it actually is not. The engine fan does in fact cool the manifold and turbo, genuinely allowing you more before you have to worry when approaching upper limits. that is what the engine fan is for... To cool the engine and its external components and extend its work range without things getting too hot. Because of this, the pyro is still an accurate measurement of overall heat accumulation on the outside of the manifold.

How you mount the probe and where you place it, and the clamp(s) on it effects its accuracy greatly, so it is a good idea to use a temp gun to verify its accuracy after installing it if your not quite sure. A second clamp or re-positioning it is sometimes necessary to get an accurate reading.

The disadvantage to having the probe set this way is that it is not as accurate for troubleshooting or custom tuning the engine, however it will still give an average sort of offset figure that will still tell you if something is too far out of place. It will give a relative reading that is almost always in the same "ball-park" temp zone, and if something changes actual EGT's, you will still see it indirectly with some delay. At best, it can only be used as a "good enough" device as far as troubleshooting goes but is better than nothing.

The Advantages of having it on the outside of the manifold are directed solely at the driver for most of its use. This allows the driver to monitor the heat buildup of the engine and turbo as they climb large hills, pull heavy loads, and go down the road in varying conditions. It lets them know if after 5 minutes of a hard pull, if the turbo or manifold temps are starting to reach their upper limits, or if engine is in a heavier strain than usual. Its best advantage to the driver though is fuel economy, as a second to the boost gauge itself.

As a driver, if the pyro gauge probe is mounted inside the exhaust manifold, and reading only EGTs, then after a few days of watching it, you quickly realize that the EGT gauge simply follows behind the boost gauge. This pretty much makes it useless for fuel efficiency OR for telling you when you might need to turn on that engine fan or drop another gear. it is important to know when to let that turbo cool off a bit when your climbing cabbage, veil, 4'th july, Donner, Grapevine, or any other really large mountain. -- This is especially important if you have de-mandated your truck and the exhaust/engine temps are going to be notably hotter.

When considering fuel economy, monitoring the overall "heat buildup" is also very useful. One can think of it as "the fire in their furnace", and the lower you keep it at all times, the more fuel efficient you are when doing the same work. Whatever trick you can do (aside from turning on the engine fan and cooling it off when it is not necessary) that keeps it as low as possible, always yields the best fuel mileage.


Some truck owners have both. --

I have met my share of people who have both. Most say that the manifold temps are about 50-75 degrees cooler during a long hill climb than the actual EGT reading, so that is where I get my comments above from, and the general consensus of the people who do have both, say the outside of the manifold is more helpful towards driving, saving fuel, and monitoring when the turbo or outside of engine is getting hot. Most also say they don't even use the actual EGT gauge after while but rather prefer the manifold readings, but then again, those same "most" are not using the engine outside its designed limits or doing their own custom tuning either.

- It would come down to an argument between a seasoned driver and what they want vs a mechanic who is only looking at the troubleshooting and limit protection, only seeing it as an "I didn't want to drill a hole" aspect. Well, i can tell you that it has nothing much to do whit not wanting to drill a hole somewhere at all. It has to do with "What do YOU need it for long term on YOUR OWN TRUCK?" -- That is why it is always a debate, and that is why not every applications is the same. If someone is still undecided on it, they can always buy 2 probes (or perhaps even 3), put them on a switch, and select between them with one gauge.


After reeding all of this, it all comes back to the 2 questions you should ask yourself. they are still ...

* What am I hoping to measure/monitor?

* What do I plan on using that information for?

Answering those 2 questions for yourself will give you the information you need to make your decisions. i own a highway truck that currently (at time of posting) has 450-hp in it, but even if I had it set on 600HP, I would still prefer it on the outside for my own application. I already roughly know what the EGT's are, and have no need much for starring every day at what I already know. I have measured the EGTs many times in the past. it does not carry much weight for me to place that probe in the exhaust stream. On the other hand ...

My biggest single expense is fuel very year. I don't know of any O/O running their own truck down the road who's biggest expense is not. The main focus for any business owner when it comes to expenses is to focus the hardest on the biggest expenses. They re the ones that suck away all your profits the fastest. -- It would be outright dumb not to.

I place my pyro gauge on the OUTSIDE of the exhaust manifold in my own operation for the sole purpose of lowering my biggest expense -- FUEL!. Every other expense is therefore secondary to this, and therefore less important. The second reason I have a pyro gauge is for lowering the second biggest expense I have, and that is maintenance/wear. This is also why I installed a boost gauge too. Between the 2 gauges, I save tens of thousands in fuel and wear costs every year, but this is only because I drive by those gauges almost exclusively. I watch them both as much as I watch my speedometer. Because they directly effect my biggest expenses of all, they are also the primary means to controlling my profits once I have accepted a load of freight to go somewhere.

Once you connect to that trailer and take it to the other end,.. the price you got paid does not go up,.. BUT -- With proper planning,.. you can make what come out of that price go down, and that is what it is all about. Not doing everything absolutely possible in every way to drive those expenses for moving that freight down is not doing everything possible to make a decent profit. -- think about that for a while and ask yourself,.. "what can i do to make more money out of what i am already paid?".. and you will soon find that you can increase your income significantly with the right tools, driving style, and the right gauges in the dash if you follow them and watch them like a hawk.

I don't know about any one else,.. but "first up the hill" and "more hp" and "bigger, louder, more brag-about stuff" simply does not pay my bills and keep my family and household going. On the other hand, slowing down, saving fuel and other expenses in every way possible, minimizing expenses does. Screw the glory of it all,.. I would rather make the money instead.
What should the egt be with the probe clamped to the outside of the manifold?
If it is clamped to the manifold it's a waste of time and money.... By the time it shows hot, the damage could be already done.

Mount the probe in the exhaust manifold for a true reading.

If the water temp climbs past normal and the oil pressure starts to drop, back off the throttle.
(07-09-2018 )redtick Wrote: [ -> ]If it is clamped to the manifold it's a waste of time and money.... By the time it shows hot, the damage could be already done.

Mount the probe in the exhaust manifold for a true reading.

If the water temp climbs past normal and the oil pressure starts to drop, back off the throttle.

Most of your posts are very informative and helpful to others on here. Thank you for that but this is one I have to disagree with. That is unless you have bad programming in your engine, or you have the HP set so high that it can cause damage in a short period of time. A properly running engine will not be so sensitive and quick to damage itself to what you are describing at all.

Your statements are indicative of a mechanic, or someone who is trying out for truck drag-racing competition. If your own experiences are like this then I feel sorry for your engine. The first post in this thread explains it quite well.
(07-09-2018 )magaroo Wrote: [ -> ]What should the egt be with the probe clamped to the outside of the manifold?

It will vary depending on what you are using your truck for. Some generalizations here ...

Anything below 400-F it is ok to shut the truck off without worrying about carbonizing the bearing in the turbocharger. A pyro gauge on the outside of the manifold is great for monitoring when it is safe to shut the enigne off after pulling off somewhere.

Max you should see is about 900 - 950 or so when pulling hard up a hill on the outside of the manifold. As it approaches this, you should down-shift to a lower gear and use higher rpm/less torque instead to the get air moving faster and cool the engine and turbo. Most guys will do so at about 850 - 900-F.

Turning on the engine fan helps when pulling a hill if it is getting up high in temp. It will force-air cool the turbocharger and lower the manifold/turbo temps. This also helps to extend the life of the turbo.
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